A channel in which algae is bred and gently stirred with a paddlewheel.

Growing algae on sewage could generate affordable biofuels. To make this work you begin with a series of small artificial rivers where waste water flows and algae is cultured. In those ponds is a paddle wheel, which pushes the water about and mixes algae into the waste water. The shallowness of the rivers encourages sunlight and helps the algae grow. And that algae is pretty important, because it’s what gets turned into biofuel.

Most waste water treatment is expensive and requires loads of energy. By using algae, as California State Polytechnic University associate professor Tryg Lundquist does, the treatment station can produce biofuels. This would, of course, be a complete reversal of the usual fuel-guzzling properties of waste water plants.

Using algae to create biofuel is somewhat old news, and it’s proven to be expensive in the past. It could range from $250 to $500 a barrel. It would need to be around $100 a barrel to be attractive to customers. Lundquist thinks that, by using waste water, we could create it for $160 a barrel, since the creation of a product that can be solf would offset the general cost of processing waste water.

“You can use less electricity, you can recycle the water, the nitrogen and the phosphorus, you can keep mixing the algae into a fuel, and it keeps rolling on in an endless cycle,” Lundquist said.